Mazdas five-place crossover surprises us with its nimble rally-car impersonation. Now how about adding a V-6?

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OIL ANALYSIS: Opinions vary about how to judge the condition of the oil in your crankcase—beyond a cursory glimpse at its color—and how often you should change it. And will using more expensive synthetic oil extend the stuff’s life? Try this: Mail a couple-ounce sample of your used oil to Blackstone Laboratories (www.blackstone-labs.com; 260-744-2380) in Fort Wayne, Indiana, and for $22.50, the company will analyze it. The examination measures the sample for 20 different elements commonly present in motor oil. A high level of aluminum, for example, could mean accelerated engine wear. It also reveals the amounts of fuel, water, and antifreeze in the oil. Blackstone won’t recommend how frequently to change your oil, but for an additional $10, the company gauges the active additive remaining in the oil—called the total base number, or TBN—that shows if the oil is still usable. After our CX-7’s 40,000 miles, we mailed in a sample that had been used for 9100 miles. Ours had high levels of iron present, but the report attributed that to “the long oil run” and said, “Don’t be too alarmed.” And the TBN test showed our synthetic 5W30 Castrol Syntec still had life left. For such a long interval, the report concluded, “this one looks pretty good.”

FUEL-ECONOMY MINDER: GI Engineering’s Digital Fuel Mizer ($49.95; www.digitalfuelmizer.com; 734-671-4295) takes a different approach than the numerous fuel-economy quick fixes—such as fuel and oil additives—and is instead designed to teach better habits from behind the wheel. The cordless, cigarette-box-sized Mizer measures acceleration and can be mounted on any reasonably flat surface inside the car. Get too aggressive with the gas or brake, and the Mizer lights progressively from green to red, accompanied by scolding beeps. We found it fairly simple to ease away from a stop while keeping the Mizer in the green zone—far easier than keeping a hybrid in electric-only mode. But at highway speeds, even wide-open-throttle maneuvers didn’t elicit a beep, since the ability to accelerate diminishes as your speed increases. Not getting reprimanded under braking requires a light touch, however, as the brakes can far more easily exceed the Mizer’s 0.25-g range (a panic stop produces about 1.00 g). To put it to the test, we sent a staffer out on two 80-mile loops—first driving as he normally would, then minding the Mizer—and the CX-7’s fuel economy increased by 10 percent.— DV